Manhole frame assemblies located along a roadway typically include an outer frame that is disposed around an access opening which may lead, for example, to utility service distribution lines. A manhole cover, drainage grate or the like in the outer frame rests flush with the roadway surface. Ordinarily an inner frame in the form of a support insert is used in the outer frame when the roadway is resurfaced with an added layer of paving material. In the case of a manhole cover, for example, the support insert raises the level of the manhole cover to the new street level. Support inserts occupy the position where the manhole cover originally rested, typically on the rim of the outer frame.
Manhole frame assemblies may be provided with locking mechanisms to prevent unauthorized personnel from removing the cover, for example, and from removing the support insert from the outer frame. As shown in U.S. Pat. No. 4,969,770, the locking mechanisms for locking the support insert to the outer frame typically include fasteners which engage the underside of the rim. Workers may have difficulty securing the inner frame since they must reach under the rim to tighten the fasteners. Tools may be dropped into the access opening and lost in the process. Moreover, such fastening devices are only able to apply a limited force to the underside of the rim and to the insert.
Manhole frame and cover assemblies are currently unable to satisfactorily prevent "inflow", a combination of storm water and other street surface liquids, from entering the access opening. This inflow may consist of billions upon billions of gallons of excess street surface liquids. Once the inflow enters the manhole frame it gains entry into utility services such as sanitary sewer distribution lines, where it burdens wastewater treatment plants, and gas, electric or telecommunications underground vaults. The inflow is a problem because it mixes with the effluent in sanitary sewers, resulting in costly additional wastewater treatment.
An additional problem is presented when the inflow reaches other utility service areas normally found in gas, electric or telecommunications distribution lines. These service areas have concrete manhole casements that do not have an individual drainage system and thus, are partially or completely filled with inflow. Such installations often require extensive vacuum pumping to remove the inflow before workmen can safely enter the manhole to perform the required maintenance or other utility service.
Manhole frame assemblies are normally comprised of metal castings, generally produced by cast iron foundries, using sand casting molds. These casting methods are used to produce manhole components in cast ductile iron, grey cast iron, or the like. Castings made from these casting processes create difficulties in duplicating nearly exact castings as compared to the mold images. Non-uniform shrinkage, warpage, and the like promote dimensional instability that affects the fit between metal surfaces necessary to provide a water-tight condition.